Ethylenimine is a potential chemical intermediate for the production of linear ethyleneamine polymers and for the production of various other amines. However, because of the toxicity and carcinogenicity of ethylenimine, this material poses severe handling difficulties, which make it highly undesirable to store or transport the ethylenimine, so that desirably a process for the production of ethylenimine should begin from inexpensive starting materials, and should provide the ethylenimine in a form which permits its direct feed to the ethyleneamine production unit without intervening isolation or storage of the ethylenimine.
Various processes for the production of ethylenimine are known. For example, ethylenimine may be produced by the reaction of ethylene dichloride with anhydrous ammonia. However, this method suffers from the disadvantages of involving halide use and producing a salt by-product.
One commercially attractive process for the production of ethylenimine is the catalytic dehydration of monoethanolamine. Various catalysts capable of effecting this dehydration are known; most of the known catalysts are oxides of tungsten, tantalum or niobium, in some cases promoted with transition metals such as iron or chromium, the metal oxides usually being disposed upon a support, for example silica or alumina.
For example, U.S. Pat. No. 4,289,656, issued Sep. 15, 1981, and U.S. Pat. No. 4,358,405, both to Hayes et al., describe a dehydration catalyst and process for making an alkyleneaziridine (such as ethylenimine) from an alkanolamine (such as monoethanolamine); the catalyst contains oxides of either tantalum or niobium together with the oxides of iron and chromium, in which the ratios of the metals are: EQU M.sub.10 Fe.sub.0.5-2.9 Cr.sub.0.3-1.7
wherein M is tantalum or niobium.
U.S. Pat. No. 4,301,036, issued Nov. 17, 1981 to Childress et al., describes a dehydration catalyst for the dehydration of alkanolamines to alkyleneaziridines. This dehydration catalyst is prepared by applying a solution of a tungsten salt on to a low surface area support (usually silicon carbide), calcining the salt to tungsten oxide, and thereafter applying silica to the tungsten-coated support so as to form a coating of silica over the tungsten.
U.S. Pat. No. 4,337,175, issued Jun. 29, 1982 to Ramirez, describes a dehydration catalyst for the dehydration of alkanolamines to alkyleneaziridines. This dehydration catalyst consists essentially of an oxide of tantalum or niobium with an alkaline earth metal oxide as a promoter on an inert support, for example a low surface area, high purity alumina.
Other catalysts have been used for the production and conversion of monoalkanolamines. For example, U.S. Pat. No. 4,524,143, issued Jun. 18, 1985 to Vanderpool, describes a process for the production of linear polyethylenepolyamines from ethylenediamine and monoethanolamine using thermally activated pelleted catalyst compositions comprising zirconium silicate having phosphorus deposited thereon.
Also, U.S. Pat. No. 4,438,281, issued Mar. 20, 1984 to Johnson, describes the selective production of monoalkanolamines from alkylene oxides and ammonia over acidic inorganic catalysts, such as acidic silica-aluminas, natural zeolites and acid clays.
It has now been discovered that .beta.-hydroxyalkylamines ca be converted to the corresponding aziridines using as catalysts molecular sieves loaded with certain metals.